This invention relates to fluid systems for engines and transmissions, and more particularly, to means indicating fluid pressure in a fluid system.
In general, it is known to provide in an oil filter a bypass piston which is slidably disposed in the housing thereof. The piston is urged into a first position by a spring, and upon filter plugging, pressure buildup on such piston moves it against such spring to bring into effect the bypass system of the filter. Such a system may be used with advantage in combination with the system of U.S. Pat. No. 3,364,481, assigned to the assignee of this invention. When used in combination with such system, the piston is used to make contact with a terminal under the urging of the spring thereof, and such contact is utilized to provide that the indicator of U.S. Pat. No. 3,364,481 shows a green color. Ideally, upon blockage of the filter element, the piston moves away from such contact, to indicate a red color on the indicator. However, it has been found that pressure pulsations are imposed on the piston due to fluctuations, created by the gear pump of the oil system, causing the indicator to turn red even though the filter element is not plugged or blocked.
Of more general interest in this area is U.S. Pat. No. 3,611,337, also assigned to the assignee of this invention.